Micromachining bulk glass by use of femtosecond laser pulses with nanojoule energy

Chris B. Schaffer, André Brodeur, José F. García, and Eric Mazur

Optics Letters (2001)

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Using tightly focused femtosecond laser pulses of just 5 nJ, we produce optical breakdown and structural change in bulk transparent materials and demonstrate micromachining of transparent materials by use of unamplified lasers. We present measurements of the threshold for structural change in Corning 0211 glass as well as a study of the morphology of the structures produced by single and multiple laser pulses. At a high repetition rate, multiple pulses produce a structural change dominated by cumulative heating of the material by successive laser pulses. Using this cumulative heating effect, we write single-mode optical waveguides inside bulk glass, using only a laser oscillator.

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Micromachining using ultrashort pulses from a laser oscillator

Chris B. Schaffer and Eric Mazur

Optics and Photonics News (2001)

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In recent years femtosecond laser pulses have been used to micromachine a great variety of materials. Ultrashort pulses cleanly ablate virtually any material with a precision that meets or exceeds that of other laser-based techniques, making the femtosecond laser an attractive micromachining tool.1 In transparent materials, where micromachining relies on nonlinear absorption, femtosecond lasers allow three-dimensional microfabrication with submicrometer precision. These lasers can produce three-dimensionally localized refractive index changes in the bulk of a transparent material, opening th door to the fabrication of a wide variety of optical devices. Until recently, micromachining of transparent materials was believed to require amplified laser systems. We have found, however, that transparent materials can also be micromachined using tightly focused trains of femtosecond laser pulses from an unamplified laser oscillator. In addition to reducing the cost and complexity of the laser system, femtosecond laser oscillators enable micromachining using a multipleshot cumulative effect.We have used this new technique to directly write singlemode optical waveguides into bulk glass.

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Time-decorrelated multifocal micromachining and trapping

David N. Fittinghoff, Chris B. Schaffer, Eric Mazur, and Jeffrey A. Squier

IEEE Journal of Selected Topics in Quantum Electronics (2001)

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Temporally decorrelated multifocal arrays eliminate spatial interference between adjacent foci and allow multifocal imaging with the diffraction-limited resolution of a single focus, even for foci spaced by less than the focal diameter. In this paper, we demonstrate a high-efficiency cascaded-beamsplitter array for producing temporally decorrelated beamlets. These beamlets are used to produce a multifocal microscope with which we have demonstrated two-photon fluorescence imaging, multifocal micromachining of optical waveguides, and multifocal optical trapping.

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Minimally disruptive laser-induced breakdown in water

Eli N. Glezer, Chris B. Schaffer, Nozomi Nishimura, and Eric Mazur

Optics Letters (1997)

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We produce minimally disruptive breakdown in water by using tightly focused 100-fs laser pulses and demonstrate the potential use of this technique in microsurgery of the eye. Using time-resolved imaging and piezoelectric pressure detection, we measure the magnitude and speed of propagation of the pressure wave produced in the breakdown. Compared with breakdown with longer pulses, here there is a much lower energy threshold for breakdown of 0.2 mJ , a smaller shock zone diameter (11 mm for 1-mJ pulses), and consistent energy deposition.

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Programmable shaping of ultrabroad-bandwidth pulses from a Ti:sapphire laser

Anatoly Efimov, Chris Schaffer, David H. Reitze

Journal of the Optical Society of America (1995)

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We have used a commercially available liquid-crystal spatial light modulator within a reflective optics pulse-shaping apparatus to shape ultrashort pulses with temporal resolution approaching 10 fs. Using the spatial light modulator as a phase modulator, we produce a variety of complex ultrafast waveforms, including odd pulses, high repetition rate (.23 THz) pulse trains, and asymmetric pulse trains. We also show that it is possible to compensate for large amounts of high-order phase dispersion (in excess of 60p) by appropriate cubic- and quartic-phase modulations of the pulse. Finally, we examine the limitations of shaping ultrabroad-bandwidth pulses. We find that, for specific classes of waveforms, Fourier-transform pulse-shaping techniques can be used for pulses with 5-fs durations, which exceed the current state of the art in ultrashort pulse generation. However, synthesis of general waveforms with 5-fs resolution will require compensating for nonlinear spatial dispersion of frequency in the masking plane.

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